Process for the manufacture of a zeolite

ABSTRACT

In the manufacture of Beta zeolite, good yields result from a high ethene pressure, advantageously accompanied by synthesis gel ageing and low aluminium content.

This application is a 371 of PCT/EP94/02458.

This invention relates to a process for the manufacture of a zeolite,especially to one suitable for use as an absorbent or catalyst, to thezeolite produced by the process, and to organic reactions, especiallyoxidations of hydrocarbons, catalysed thereby.

Zeolite Beta is a large pore, high silica zeolite material firstdescribed in 1967, in U.S. Pat. No. 3,308,069. Because of its large poresize, based on 12-membered rings, it is useful as a catalyst forreactions involving larger organic molecules than can be accommodated inthe pore of the more commonly used ZSM-5, 10-membered ring, zeolitecatalysts.

The previously proposed processes for the manufacture of the catalysthave all employed synthesis mixtures containing cations of an alkalimetal; indeed, in an article by Camblor et al, Zeolites, 1991, 202 to210, it is suggested that the presence of alkali metal cations isessential for the formation of the zeolite. Certainly, in the existingprocesses yields in the absence of alkali metal cations are very low.

The presence of alkali metal cations in the synthesis mixture is,however, disadvantageous, especially when the zeolite is to be used asan acidic catalyst, since any necessary post-calcination treatment ismade longer by the presence of substantial alkali metal concentrations.

The present invention is based on the observation that if ethene ispresent in contact with a Beta-forming synthesis mixture during thehydrothermal treatment Beta zeolite is obtained in good yields.

The present invention accordingly provides in a first aspect a processfor the manufacture of a Beta zeolite in which at least a part of ahydrothermal treatment of a Beta zeolite-forming synthesis mixture iscarried out under an ethene-containing atmosphere at a pressure of atleast 20 bar and advantageously under an ethene partial pressure of atleast 5 bar.

In a second aspect, the invention provides a process for the manufactureof a Beta zeolite in which at least a part of a hydrothermal treatmentof a Beta zeolite forming synthesis mixture is carried out in thepresence of at least 0.1 mole of ethene per mole of tetraethylammoniumcations. Advantageously, the mole ratio of ethene:tetraethylammonium isin the range 0.1 to 1:1.

As a Beta forming synthesis mixture, there is typically used a mixturecomprising a source of silicon, a source of aluminium, water, and asource of tetraethylammonium cations. The aluminium may, however, bereplaced wholly or in part by other cations, for example gallium, boron,or iron.

The synthesis mixture is advantageously substantially free from alkalimetal cations; by substantially free is meant the absence of more alkalimetal than is inevitably present in commercial supplies of the essentialcomponents. If alkali metal ions, e.g., sodium or potassium ions, arepresent, they are advantageously present in a molar proportion of SiO₂:M⁺ of 1: at most 0.5.

Advantageously, the synthesis mixture has a molar composition within thefollowing ranges: SiO₂ (1); Al₂ O₃ (0.0005 to 0.1); H₂ O (10 to 100) andTEAOH (0.01 to 1).

Advantageously, the Si:Al molar ratio is within the range of from 50 to200:1.

Preferred sources of the components are: for silicon, colloidal silica,advantageously a colloidal silica substantially free from alkali metalcations, or a tetraalkylammonium orthosilicate; and for aluminium,aluminium powder. If the aluminium is replaced by other cations,suitable sources are, for example; gallium nitrate or oxide, boric acidor an alkoxide thereof, e.g., B(OC₂ H₅)₃, or ferric nitrate. Thetetraethyl ammonium cations are advantageously provided by TEAOH.

If desired or required to assist dissolution of any reactants, hydrogenperoxide may be present in the synthesis mixture.

Advantageously, especially if it contains hydrogen peroxide, thesynthesis mixture is aged between its formation and the hydrothermaltreatment. Ageing may be carried out at room temperature or at elevatedtemperatures, for example at from 60° to 90° C., advantageously about70° C., the ageing time being from 2 to 24 hours, depending inversely onthe temperature. A preferred ageing treatment comprises initial roomtemperature ageing for from 12 to 18 hours, followed by elevatedtemperature ageing, e.g., at 70° C., for from 2 to 4 hours.

Elevated temperature ageing also causes evaporation of water from thesynthesis mixture, thereby producing a synthesis gel of a concentrationadvantageous for hydrothermal treatment. If desired, or required, theaged gel may be diluted before treatment, e.g., with ethanol. If ethanolis added, it is advantageously present in the synthesis mixturesubjected to hydrothermal treatment in a proportion of at most 2 molesper mole of SiO₂.

The synthesis mixture, preferably aged, is advantageously subjected tohydrothermal treatment at a temperature within the range of from 120° C.to 200° C., preferably from 130° C. to 150° C., under the pressureregime as indicated above, advantageously for a time in the range offrom 1 hour to 30 days, preferably from 6 days to 15 days, untilcrystals are formed. Hydrothermal treatment is advantageously effectedin an autoclave.

While not wishing to be bound by any theory, it is believed that underthe conditions prevailing under the hydrothermal treatmenttetraethylammonium ions decompose and are unavailable to form a templateeffective in zeolite formation. By carrying out the treatment in thepresence of ethene, a decomposition product, the equilibrium of thedecomposition reaction is displaced and more tetraethylammonium ionsremain available to act as templates.

In any event, by carrying out at least part of the hydrothermaltreatment in the presence of ethene, a higher zeolite yield may beobtained or a lower proportion of tetraethylammonium ions may beincluded in the synthesis mixture. Advantageously, ethene is present inthe reaction vessel from the commencement of the hydrothermal treatment.

Advantageously, the ethene partial pressure is at least 5 bar,preferably at least 20 bar, and most preferably at least 30 bar, for atleast a part of the period of hydrothermal treatment. Also,advantageously, the total pressure is at least 30 bar, and preferably atleast 40 bar. Advantageously, the ethene partial pressure is at least80%, preferably at least 90%, of the total pressure.

After crystallization has taken place, the synthesis mixture is cooled,and the crystals are separated from the mother liquor, washed and dried.

To eliminate the organic base from the crystals, they are advantageouslythen heated to from 200° to 600° C., preferably about 550° C., in air,for from 1 to 72 hours, preferably about 12 hours.

The resulting calcined product may either be used as such or subjectedto further treatment e.g., by acid, for example, HCl, or by cationexchange, e.g., to introduce nickel. The product may be post-treated, asby steaming.

The Beta zeolite produced by the process of the invention may be highlycrystalline and has the typical Beta zeolite IR absorption bands at 575and 525 cm⁻¹ and X-ray diffraction spectrum.

The zeolite produced according to the invention is useful as a catalystin all reactions where an acidic catalyst is effective, especially inthe production and conversion of organic compounds, for examplecracking, hydrocracking, dewaxing, isomerization (including e.g., olefinbond isomerization and skeletal isomerization e.g., of butene),oligomerization, polymerization, alkylation, dealkylation,hydrogenation, dehydrogenation, dehydration, cyclization andaromatization. The present invention therefore provides a process forthe production or conversion of an organic compound comprising the useof a zeolite catalyst prepared in accordance with the invention. Thezeolite can also be used (either as initially prepared or in a modifiedform) in a selective adsorption process e.g., a separation orpurification.

The following Example illustrates the invention.

EXAMPLE 1

256 g of distilled H₂ O were cooled to 5° C., and 103 ml of H₂ O₂ (35 wt% in H₂ O) were added. The resulting solution was stirred for 3 hours at5° C.

The aluminium source, 0.3859 g Al powder, and 366 g of the template,TEAOH (40% in H₂ O), were combined in a beaker, covered to preventevaporation, and heated at 80° C. for 2 hours. After dissolution ofaluminium, 183 ml of distilled water were added. The resulting solutionwas cooled to 5° C.

The two solutions were mixed, and the resulting solution stirred at 5°C. for another hour. Afterwards, 61 g of colloidal silica (Aerosil, 200m² /g) are added, and stirred for 18 hours at room temperature. A gelwith the following molar composition is thus obtained; SiO₂ :1; TEA₂O:0.49; Al₂ O₃ :0.007; H₂ O:28.

Subsequently, the solution was kept at 70° C. for 2 hours, and thenallowed to cool to room temperature. Before transferring the solution toa 1000 ml, ptfe-lined, stainless steel autoclave, 61 ml of ethanol wereadded. The synthesis mixture occupied about 95% of the volume. Gas phaseanalysis showed a high ethene content in the head-space.

The autoclave was kept at 140° C. without agitation. After 11 days,pressure had risen to 50 bar. The crystals were separated from themother liquor and washed by centrifugation at 13,000 rpm. After dryingat 60° C., the organic template was removed from the zeolite pores bycalcination at 550° C. in air for 12 hours.

X-ray diffraction study of the product before calcination showed that ithad pure Zeolite Beta crystal structure. The yield, expressed as theweight of solids after calcination as a proportion of the total of SiO₂and Al₂ O₃ in the gel, was 42%. The Si:Al ratio (²⁷ Al-NMR) was 36:1.

We claim:
 1. A process for the manufacture of Beta zeolitecomprising:(a) Providing a Beta Zeolite-forming synthesis mixture; and(b) Hydrothermally treating said Beta Zeolite-forming synthesis mixtureto produce Beta Zeolite; wherein at least a portion of the hydrothermaltreatment of step (b) is carried out under an ethene-containingatmosphere at a total pressure of at least 20 bar.
 2. The process ofclaim 1 wherein at least part of the hydrothermal treatment is carriedout under an ethene partial pressure of at least 5 bar.
 3. The processof claim 2 wherein the ethene partial pressure is at least 20 bar. 4.The process of claim 3 wherein the ethene partial pressure is at least30 bar.
 5. The process of claim 1 carried out at a total pressure of atleast 30 bar.
 6. The process of claim 1 wherein the synthesis mixturecomprises water, a source of silicon, a source of aluminium, and asource of tetraethylammonium ions.
 7. The process of claim 6 wherein themolar composition of the synthesis mixture is within the followingranges: SiO₂ (1); Al₂ O₃ (0.0005 to 0.1); H₂ O (10 to 100); TEAOH (0.01to 1).
 8. The process of claim 1 wherein the synthesis mixture containscolloidal silica.
 9. The process of claim 8 wherein the colloidal silicais substantially alkali metal-free.
 10. The process of claim 1 whereinthe synthesis mixture contains a tetraalkylorthosilicate.
 11. Theprocess of claim 1 wherein the synthesis mixture contains hydrogenperoxide.
 12. The process of claim 1 wherein the synthesis mixture isaged between its formation and the hydrothermal treatment.
 13. Theprocess of claim 12 wherein at least part of the ageing is carried outat room temperature.
 14. The process of claim 2 wherein at least part ofthe ageing is carried out at an elevated temperature.
 15. The process ofclaim 1 wherein the synthesis mixture subjected to hydrothermaltreatment contains ethanol, in a proportion of at most 2 moles per moleof SiO₂.
 16. The process of claim 1 wherein hydrothermal treatment iscarried out at a temperature within the range of from 120° C. to 200° C.17. The process of claim 1 wherein hydrothermal treatment is carried outfor from 1 hour to 30 days.
 18. The process of claim 4 wherein afterhydrothermal treatment the resulting Beta Zeolite is recovered andcalcined in air at from 200° to 600° C., for from 1 to 72 hours.
 19. Theprocess of claim 18 wherein the calcined Beta Zeolite is treated with anacid or a base, or is steamed.
 20. A process for the manufacture of BetaZeolite comprising:(a) Providing a Beta Zeolite-forming synthesismixture containing tetraethylammonium cations; and (b) Hydrothermallytreating said Beta Zeolite forming synthesis mixture to produce BetaZeolite; wherein at least a portion of the hydrothermal treatment ofstep (b) is carried out in the presence 0.1 mole of ethene per mole oftetraethylammonium cation.
 21. The process of claim 20 wherein the moleratio of ethene:tetraethylammonium is in the range 0.1 to 1:1.